The present invention relates to the use of alkali metal pyrophosphates and alkaline earth metal pyrophosphates which are particularly adapted to reducing water hardness. The alkali metal pyrophosphate and alkaline earth metal pyrophosphate may be used alone as an additive product or formulated into a complete detergent composition. Additive products are intended to supplement the consumer's regular detergent product as a presoak or by direct addition to the wash solution with the consumer's detergent. The detergent composition of the present invention includes an organic detergent as an additional component to the alkali metal pyrophosphate and an alkaline earth metal pyrophosphate.
Builders are important to detergent compositions in that a builder functions to control water hardness. If an ineffective builder or ineffective amounts of a builder are used cleaning performance by the detergent is lessened. The lack of builder capacity is evidenced by measuring the reflectivity of fabrics washed in hard water versus control fabrics washed in the absence of hard water where reflectance is greater.
Detergent builders have for the most part been classified as sequestering or precipitating. Sequestering builders include for example, such materials as water-soluble tripolyphosphate, citrate, ethylene diamine tetraacetate, and organic phosphonates. Alkali metal pyrophosphates are also classed as sequestering builders.
Precipitating builders are materials such as the alkali metal carbonates, bicarbonates, sesquicarbonates, silicates, aluminates, oxylates, and fatty acids, particularly the sodium and potassium salts.
The distinction between precipitating and sequestering builders, is stated to be whether or not a significant amount of precipitate is formed when the builder is used in an amount sufficient to combine with all of the calcium ions in solution. A builder such as sodium tripolyphosphate when used at a level of about 0.06% by weight in a solution containing 7 grains of calcium hardness is not classed as a precipitating builder as no precipitation occurs. As the tripolyphosphate has controlled the hardness, the mechanism is sequestration. Sodium carbonate, however, is classed as a precipitating builder when used at the same concentrations as the sodium tripolyphosphate in a 7 grain solution of calcium ions as the carbonate will eventually precipitate as calcium carbonate, even though the rate of precipitation is slow.
Precipitating builders such as sodium carbonate which exhibit extremely slow rates of precipitation with calcium ions are frequently insufficient to prevent intereference by the calcium ion with the detergent thereby impairing the cleaning of the fabrics. This intereference takes place primarily at the site of body soil stains where the calcium ions become affixed to the carboxyl radicals in the fatty acids of the body soil. Another way in which the calcium ions interfere with the detergency process is that they combine with the detergent component to lessen the detergents effective concentration. For instance, alkyl benzene sulfonates are anionic detergents which may be precipitated by calcium ions to the extent that on a stoichiometric basis one mole of calcium ion solution will precipitate 2 moles of alkyl benzene sulfonate, thus substantially lowering the amount of detergent active available for cleaning.
As was previously mentioned the sodium carbonate would if given sufficient amount of time precipitate most of the calcium ions. During the course of a wash cycle which is generally from 10 to 12 minutes, the calcium ions do not precipitate but predominantly associate as a soluble species in a 1:1 ion pair with the carbonate anion. This soluble calcium complex has a binding constant much less than that found in the calcium tripolyphosphate sequestered complex. To improve the effectiveness of sodium carbonate as a detergent builder it has been suggested in Belgium Pat. No. 798,856 issued Oct. 29, 1973, herein incorporated by reference, that a crystallization seed such as calcium carbonate be included in the composition. The use of the crystallization seed provides a two-fold benefit. First, the calcium ions in the wash solution are rapidly depleted by the precipitation of the calcium and carbonate ions onto the surface of the crystallization seed, and second, that once precipitated upon the crystallization seed the calcium ions are no longer free to interfere with the organic detergent components.
It was previously stated that the alkali metal pyrophosphates with which the present invention is concerned, are classed as sequestering builders. Sodium pyrophosphate is the equivalent of sodium tripolyphosphate in that both possess the ability to sequester one mole of calcium hardness per mole of the respective polyphosphate anion. This sequestration by pyrophosphate is extremely rapid and permanent in that the calcium ions once sequestered do not to any appreciable extent become free again. Indeed sodium pyrophosphate in a composition of limited phosphorus content is more advantageous to use than tripolyphosphate because the molecular weight of the pyrophosphate is lower than that of the tripolyphosphate thus allowing more moles of pyrophosphate anion to be present than of the tripolyphosphate anion at a given phosphorus content.
It has now been found that alkali metal pyrophosphates are made much more effective in their building capacity when used in conjunction with finely divided particles of calcium pyrophosphate. It was previously stated that the alkali metal pyrophosphates were previously known for their use in detergent product as sequestrants of water hardness. While not wishing to be bound by any particular theory it appears that the calcium pyrophosphate causes the alkali metal pyrophosphates to precipitate rather than only sequester calcium ions in the wash. Some of the effect of the calcium pyrophosphate alone may be to assist in increasing the reflectivity of the washed fabric.
Whereas sodium pyrophosphate sequesters calcium ions on a 1:1 molar basis, it will precipitate as the dicalcium salt on the finely divided calcium pyrophosphate in a ratio of 2 moles of calcium ion per mole of soluble pyrophosphate. Thus substantially larger amounts of calcium ion can be controlled by precipitation than by sequestration.
It is thus an object of the present invention to prepare a detergent additive or complete detergent composition containing an alkali metal pyrophosphate as a detergent builder.
It is yet a further object of the present invention to prepare a detergent composition or detergent additive containing calcium pyrophosphate.
Yet a further object of the present invention is to prepare a detergent additive or complete detergent product containing as a builder system an alkali metal pyrophosphate which is of an increased effectiveness in depleting water hardness and maintaining whiteness through the use of calcium pyrophosphate.
Percentages and ratios throughout the specification and claims are by weight unless otherwise indicated. Temperatures are by degrees Fahrenheit unless noted otherwise.